Navigation systems for tracking and navigating an instrument in space are known. Such systems may be based on electromagnetic, optical, acoustic and other physical principles. For example, a navigation system can be used to track an instrument during an interventional medical procedure on a patient. Such tracking can determine the instrument's position relative to a target organ without physically viewing the instrument. The tracking may include direct tracking of a particular instrument section external to the patient or tracking of a distal point of the instrument within the patient. In an example, the external section is a proximal end of a long and substantially rigid instrument, while the distal point is a distal instrument end or “tip”.
Tracking of the 3D position and spatial inclination of an instrument through combined ultrasound (US) time of flight (TOF) and time-stamping is also known. US TOF based positioning methods require accurate synchronization between a transmitter and a receiver to compensate for respective clock inaccuracies and drift. The synchronization uses RF transmissions. Such methods suffer from several problems. 1) the RF propagation is assumed instantaneous and thus delay errors are introduced and affect readings of TOF; 2) the use of a small number of transmitters involves line-of-sight (LOS) problems caused by obstructing objects which prevent signals from arriving at receivers; 3) while LOS obstruction may be overcome by fast sequential or simultaneous scanning over a large number of transmitters, this procedure slows the acquisition and the positioning algorithms and therefore is inadequate for tracking fast moving instruments or random hand movements of e.g. physicians in an operating room. Also, the synchronization of receiver and transmitter clocks requires initial calibration. If the RF propagation is not assumed to be of infinite speed, long sampling windows introduce ambiguities caused by reflected US waves, and 3D triangulation requires special attention to positioning of at least four transmitters in order to avoid singularities.
The guiding of an interventional tool during operation within the body is important. Conventional procedures are conducted using X-ray and/or US imaging technology to facilitate tool guidance. Typical image guided navigation systems (e.g. as described in U.S. Pat. No. 8,359,730) require dynamic reference frames to track the position of the patient. The dynamic reference frame is generally affixed to the patient in a permanent or immovable fashion. The dynamic reference frame may be used as a fiducial marker and may, therefore, be attached to the patient during the acquisition of pre-operative images. However, such markers on the body are connected to a measurement and registration unit by wires. Use of wireless transmission is problematic, since wireless-enabled markers would need transmitters that cannot be placed inside an MRI scanner. Therefore, both patient and attached markers must be fixed to the operation bed, since the reference point is set with respect to the bed.
There is therefore a need for, and it would be advantageous to have methods and systems for real time navigation and guiding of a moving instrument relative to a stationary object that do not suffer from the abovementioned problems and disadvantages